MacOS: update locate_cctool

This becomes MacOS.{install_name_tool,otool}, only do check_xcode if
xcode is installed, otherwise emit a warning

Library/Homebrew/cmd/install.rb

@@ -157,7 +157,12 @@ module Homebrew
   def perform_preinstall_checks
     check_ppc
     check_writable_install_location
-    check_xcode
+    if MacOS::Xcode.installed?
+      check_xcode
+    else
+      opoo "You have not installed Xcode."
+      puts "Bottles may install correctly, but builds will fail!"
+    end
     check_cellar
   end
 

Library/Homebrew/keg_relocate.rb

@@ -98,8 +98,8 @@ class Keg
   end
 
   def install_name_tool(*args)
-    tool = MacOS.locate("install_name_tool")
-    system(tool, *args) || raise(ErrorDuringExecution.new(tool, args))
+    tool = MacOS.install_name_tool
+    system(tool, *args) || raise ErrorDuringExecution.new(tool, args)
   end
 
   # If file is a dylib or bundle itself, look for the dylib named by

Library/Homebrew/mach.rb

@@ -154,9 +154,9 @@ module MachO
 
     def parse_otool_L_output
       ENV["HOMEBREW_MACH_O_FILE"] = path.expand_path.to_s
-      libs = `#{MacOS.locate("otool")} -L "$HOMEBREW_MACH_O_FILE"`.split("\n")
+      libs = `#{MacOS.otool} -L "$HOMEBREW_MACH_O_FILE"`.split("\n")
       unless $?.success?
-        raise ErrorDuringExecution.new(MacOS.locate("otool"),
+        raise ErrorDuringExecution.new(MacOS.otool,
           ["-L", ENV["HOMEBREW_MACH_O_FILE"]])
       end
 

Library/Homebrew/os/mac.rb

@@ -36,6 +36,22 @@ module OS
       end
     end
 
+    def install_name_tool
+      if File.executable?(path = "#{HOMEBREW_PREFIX}/opt/cctools/bin/install_name_tool")
+        Pathname.new(path)
+      else
+        locate("install_name_tool")
+      end
+    end
+
+    def otool
+      if File.executable?(path = "#{HOMEBREW_PREFIX}/opt/cctools/bin/otool")
+        Pathname.new(path)
+      else
+        locate("otool")
+      end
+    end
+
     def active_developer_dir
       @active_developer_dir ||= Utils.popen_read("/usr/bin/xcode-select", "-print-path").strip
     end